
Quoting
Mr. Knowitall
You need to ask your employer for clarification. It's possible that they're referring to a need to get the trustee to approve new hires and the expenses associated with applying for the H1B. it's possible that you misheard and that you've cleared a check on your credit associated with their offer of employment... We can only guess.
If they applied for premium processing, you would normally get a decision within 15 calendar days. The issue of your starting before you're formally approved will likely be moot as of Monday or Tuesday.